As shown in FIG. 1, generally, a refrigerator 1 is an apparatus for storing food at a low temperature, and comprises a cabinet 10 constituting storage spaces, such as a refrigerating compartment and a freezing compartment, a door (not shown) opening and closing the refrigerating compartment and the freezing compartment, and a machine part (not shown) comprising a refrigerant cycle and maintaining the stored food at a low temperature.
The cabinet 10 has an insulation material filled between exterior surfaces forming a profile and interior surfaces defining storage spaces, to thereby increase the insulation effect. For this, as shown in FIG. 2, polyurethane foam 30 is filled between the interior surfaces 20 and exterior surfaces 10 of the cabinet in an assembled state, which is formed by injecting a polyurethane foam solution therebetween and then heating and foaming it. However, there is a limitation in enhancing the insulation performance since the air transmitting heat is impregnated in the polyurethane foam 30 and due to the thermal conduction properties of the polyurethane itself.
Accordingly, in order to enhance refrigeration efficiency and energy efficiency by further blocking a heat exchange between the storage spaces in the refrigerator and external air of the refrigerator, recently, as shown in FIG. 3, an improved insulation structure has started to be used, which further comprises a vacuum insulation panel between the cabinet exterior surfaces 10 and the cabinet interior surfaces 20, in addition to an insulation part 30 formed of polyurethane foam.
Specifically, the vacuum insulation panel 40, as shown in FIGS. 4 and 5, comprises a core material 41 having panels woven from glass fibers stacked thereon, and having vacuum formed between the panels, a sealing cover 42 formed of an aluminum laminated film for sealing and covering the core material 41 so as to maintain vacuum of the core material 41, and a getter 43 formed so as to maintain the insulation performance as the vacuum insulation panel for a sufficient time by removing a gas component flowing in through the insulation sealing cover 42.
As show in FIG. 6, the sealing cover 42 is formed by stacking an outermost layer 421 and a protective layer 422 both formed of a material resistant to an external impact, a gas shielding layer 423 of A1234 material (which is referred to as “1N30” in Japan) so as to prevent an external gas or moisture from penetrating into the core material 41, and a heating-fusion bonding layer 424 formed of a butane-base LLDP material with four carbons (C).
The vacuum insulation panel 40 covers the core material 41 with the sealing cover 42 in a vacuum condition, and then heating-fusion bonds the heating-fusion bonding layer 424 on the lower surface 42b of the sealing cover 42 and the heating-fusion bonding layer 424 of the upper surface 42a thereof, both of them bonded to each other, thereby separating the core material 41 from the outside.
To separate the core material 41 more completely from the outside, the upper and lower surfaces 42a and 42b of the sealing cover 42 are heating-fusion bonded at somewhat great length. Therefore, bonding portions 42a′ and 42b′ (42′) protruded from the sides of the core material 41 are formed. The thus-formed vacuum insulation panel 40 is installed at a position, like in the refrigerator cabinet, in such a shape as shown in FIG. 7 by folding the bonding portions 42′ and inserting them therein.
However, as shown in FIG. 8, when the bonding portions 42′ are folded and installed at a predetermined position, this provides high insulation properties in the direction 98 in which the core material 41 formed of vacuum is penetrated, but the gas shielding layer 423 formed of a thin aluminum sheet having a thermal conductivity coefficient several thousand to several ten thousand times higher than that of the core material 41 is contained in the sealing cover 42. Thus, the quantity of thermal transfer through the gas shielding layer 423 is increased in the plate surface direction 99 of the sealing cover 42, thereby deteriorating the insulation properties.
As shown in FIG. 9, the bonding portions 42′ protruded from the core material 41 and heating-fusion bonded have to be folded while the constructed sealing cover 42 is inserted and installed in the refrigerator cabinet 42′. In the folding procedure, pin holes 99 are generated in the gas shielding layer 423, and thus external air flows in through the pin holes to release the degree of vacuum of the core material 41, thereby abruptly deteriorating the insulation performance of the vacuum insulation panel 40 with the passage of time.
Besides, the gas shielding layer 423 of the thus-constructed sealing cover 42 has the problem that cracks are generated even by a slight bending due to a residual stress caused by a rolling process or the like, as well as the advantage of effectively preventing an external gas or moisture from penetrating into the vacuum insulation panel 40.
Therefore, with the sharp increase in oil price and the necessity of energy saving, there is an increasing demand for the vacuum insulation panel 40 that is applicable to various products, including a freezer and a refrigerator, and has a more excellent insulation performance.